1. Field of the Invention
The present invention relates to a double-layer pipe bend for a pipeline for transporting solids, particularly concrete, to which liquids have been admixed. The pipe bend includes a wear-resistant inner pipe and an outer pipe of weldable material surrounding the inner pipe. Connecting flanges at the ends of the pipe bend are welded to the outer pipe. The outer diameter of the inner pipe and the inner diameter of the outer pipe are selected in such a way that the inner pipe can be inserted in the outer pipe without deformation. An intermediate layer which supports the inner pipe is provided between the outer pipe and the inner pipe.
2. Description of the Related Art
The magazine "Maschinenmarkt", Wurzburg, 84 (1978) 12 discloses on page 200, FIG. 5, and in the left and center column on page 201 describing FIG. 5, a double-layer pipe bend for a pipeline for transporting solids, particularly concrete, to which liquids have been admixed, wherein the pipe bend is composed of a lining element of artificial basalt, of a thin-walled steel pipe surrounding the lining element and connecting flanges at the ends which are apparently welded to the steel pipe.
The outer diameter of the lining element and the inner diameter of the steel pipe are selected in such a way that the lining element can be inserted in the steel pipe without deformation. In addition, a mortar layer is provided between the steel pipe and the lining element for supporting the lining element in the steel pipe.
The pipe bend described above has the disadvantage that it is difficult to mount the lining element in the steel pipe by means of the hardening mortar because the mortar is applied to the lining element hydraulically with an special method which, however, is not described in detail.
The known pipe bend has the further disadvantage that, due to the friction between the transported medium and the lining element, the lining element can be displaced in axial direction of a pipeline relative to the steel pipe. This axial displacement of the lining element relative to the steel pipe may then lead to a mortise joint-type connection between successive pipe bends or between a pipe bend and a straight pipe. As a result, it is nearly impossible to remove a pipe bend from a pipe line radially as it is repeatedly required in practical operation. Even if the requirement is met that several pipes can be removed from a pipeline with at least one pipe bend although only the pipe bend has to be removed, there still is the problem that portions of the axially displaced lining elements project freely axially beyond the steel pipes. These portions are of a very sensitive material and, therefore, are extremely susceptible to being damaged, particularly in view of the fact that the pipe bend is subjected to high loads during operation.
In addition, if there are several axially displaced lining elements, it is possible that at the rearward end of the displaced lining elements in conveying direction an extremely wide gap is formed between a lining element which has not yet been displaced and the next already displaced lining element. Accordingly, in the area of the gap there is the increased danger of turbulence of the transported medium which, in turn, leads to extremely high wear.
The known pipe bend has the further disadvantage that the wall thicknesses of the line element are the same in all areas. As a result, it is not possible to take into account the particular operating conditions of those pipe bends which are located at the conveying end of a concrete conveying arrangement which includes pipe sections with several bends, such as, self-propelled concrete pumps. This is because these pipe bends are subjected to strong impact-like loads by the concrete which is transported through the pipe lines. Consequently, these pipe bends have a significantly shorter service life than the adjacent straight pipe sections.
German Offenlegungsschrift 33 15 819 discloses a straight pipe element composed of an outer steel pipe and a pipe of plastic material inserted in the steel pipe. The annular gap between the plastic pipe and the outer steel pipe is filled by a hardening filler material. In addition, a flange is arranged at each end of the steel pipe. One end of the plastic pipe is extended over a sleeve at the other end of the steel pipe.
German patent 8 05 637 discloses a pipe bend for stowing lines composed of three segments. Each individual segment has a wearing insert of asymmetrical wall thickness which is supported by two housing halves of equal construction which can be coupled to each other by means of snap closures. The housing halves are to be made of light metal.
German Auslegeschrift 10 95 768 shows the connection between two double-layer pneumatic stowing pipes. The material of the two layers is not described. It is also not described how the inner layer can be inserted in the outer layer without deformation.